An unusual outbreak of measles occurred in 1982 in a pediatrician''s office in Muskegon, Michigan, USA. Three children, who had arrived at the office 60-75 min after a child with measles had departed, developed measles. Using a model based on airborne transmission, it is estimated that the index patient was producing 144 U of infection (quanta)/min while in the office. Characteristics such as coughing, increased warm air recirculation and low relative humidity may have increased the likelihood of transmission. Adequate immunization of all patients and staff, respiratory isolation and prompt care of all suspected cases, and adequate fresh-air ventilation should decrease the risk of airborne transmission of measles in this setting. Airborne transmission may occur more often than previously suspected, a possibility that should be considered when evaluating current measles control strategies.